Non-alcoholic steatohepatitis (NASH) is a major public health problem that can lead to hepatocellular carcinoma and cirrhosis requiring liver transplantation. NASH is an increasingly common condition that is rising in prevalence in parallel with associated conditions such as obesity and type II diabetes. There are no approved treatments for NASH and the mechanisms of disease progression remain largely unknown. Endoplasmic reticulum (ER) stress is an adaptive cellular response to a variety of stressors including excess intrahepatic triglyceride. In experimental models, excessive ER stress promotes apoptosis, further lipid accumulation and activation of pro-inflammatory pathways such as NF-KB thought to be important in the pathogenesis of NASH. Feeding mice a methionine-choline deficient (MCD) diet induces steatohepatosis that resembles human NASH and liver injury is exacerbated in db/db mice fed this diet. The mechanisms by which the MCD diet leads to lipid accumulation and liver injury are incompletely understood. Thus, Specific Aim #1 will define mechanisms of lipid accumulation and liver injury in the db/db mouse fed this diet. Preliminary data from our laboratory illustrate the presence of robust ER stress signaling in both MCD fed db/db mice and human NASH liver biopsy samples. We hypothesize that in this experimental model, ER stress stimulates pathways important to progressive liver injury. Therefore, Specific Aim #2 will show that ER stress is a prominent feature of MCD diet induced steatohepatitis by examining key elements of the PERK and IRE-1 ER stress pathways, and then demonstrate improvement in steatohepatitis through attenuation of ER stress using tauroursodeoxycholic acid (TUDCA). Specific Aim #3 will confirm these findings in hepatocytes exposed to MCD medium and we will determine if c-Jun N-terminal kinase (JNK) mediated NF-KB activation is IRE-1 dependent in this model system. NASH is an important field of research and both my mentor and institution fully support this research proposal. They have made protecting time a priority during the term of my current grant and will continue to do so should I be selected for funding. If awarded a K08, I will apply for an R01 in the last year of the award. Non-alcoholic steatohepatitis (NASH) is a major public health problem and a growing indication for liver transplantation. The experiments outlined in this grant proposal will explore the role of endoplasmic reticulum stress in the development of liver injury in a mouse model of NASH. We hope that insight gained from this work will identify factors responsible for the development of NASH that will guide future experiments and ultimately therapy in human NASH.